Conventionally, optical disks are marked on a data side using laser activated material to produce darkened spots to indicate data. The darkened spots are read by an optical disk drive. The optical disk drive reads the data by emitting light at the disk and sensing whether the light is reflected back.
In order to more fully utilize the space available on an optical disk, it is desirable to fit as much data on a disk as possible. To achieve this goal, the spot size is reduced to increase the density of data stored. The spot size is reduced as much as possible while still maintaining the ability to read and write the data accurately.
Optical disks may also be labeled with an image. A laser-activated material is applied to the disk on the label side. The laser-activated material is darkened or marked by exposure to the laser in an optical disk drive.
The amount of time it takes to create or print a label on the laser-activated material is a function of the velocity at which the disk rotates and the width of the tracks on the disk. Higher velocities reduce the printing time, but there is an upper limit to the velocity at which the disk may be rotated and the labels printed.
Conventionally, wider tracks reduce the print time, but allow unmarked space between the tracks. The wider tracks are often spaced further apart than the width of a well-focused marking beam in order to decrease the time needed to create the label. The unmarked space visually combines with the marked space to give the appearance of a less than completely marked area. Where the unmarked space is white or another light color and the marked space is intended to be black, the result may appear to be less than completely black.
A measure of the amount of light absorbed is an optical density (OD). An area that appears to a user to have full absorption appears black and has an OD of 1.2. Higher OD values are possible, but they do not appear to be darker to a user. Conventional use of wider tracks often results in an OD of less than 1.2.
Narrower tracks result in more tracks per inch on the disk, which create darker images, as there is less unmarked space between the tracks. However, narrower tracks require longer printing times as there is more surface area for the laser to cover. Therefore, there is a tradeoff between printing speed and OD. A label printed using conventional techniques may be created using narrower tracks and having an OD of at least 1.2, but it will take longer to print than a label created using wider tracks and having an OD less than 1.2.